Conventionally, when drawing a graphic entity object, two imaging models are usually used: substitute imaging model and transparent imaging model.
In the substitute imaging model, a graphic entity object newly drawn on a page completely replaces a background content at the location of the graphic entity object. That is, a final color of a point at the location is determined by a last graphic entity object drawn at the location. In the transparent imaging model, a transparent graphic entity object newly drawn on a page and a prior background content at the location of the graphic entity object are mixed. That is, the final color of a point at the location is determined by all graphic entity objects drawn at the location.
However, in the transparent imaging model, graphic entity objects newly drawn on a page may first need to be assembled. Since no prior determination is made on whether each of the graphic entity objects newly drawn on the page is a transparent image or a nontransparent image, calculations need to be performed during the assembling process on all graphic entity objects newly drawn in the page. Therefore, the calculation is complicated.
Moreover, in the transparent imaging model, transparency calculation needs to be performed on a graphic entity object newly drawn on a page and a prior background content at the location of the graphic entity object. When the resolution of the background content is high, there may be a large amount of data in the transparency calculation, and thus the calculation may be complicated, and time consuming.